The invention relates to a longitudinal displacement unit for driveshafts. Driveshafts with such longitudinal displacement units are used in the driveline in engineering or vehicle construction.
U.S. Pat. No. 4,981,459 discloses a longitudinal displacement unit for driveshafts with a first shaft element that includes an outer face provided with circumferentially distributed first grooves that extend parallel to a longitudinal axis. A second shaft element is provided with a through-bore that extends along the longitudinal axis and receives the first shaft element. In the through-bore, there are provided second grooves that are positioned opposite the first grooves and extend parallel to the longitudinal axis. In the through-bore, between the first shaft element and the second shaft element, there is provided a sleeve-shaped cage that guides balls that engage grooves arranged opposite one another. The groove run-out, or the end of a recess in the outer face of the first shaft element that adjoins the grooves, forms a delimiting means or a stop for the balls, which are held close to the associated end of the cage. The travel of the cage toward the first shaft element is thus delimited. If there is provided a groove run-out, this can lead to jamming. If there is provided a circumferential recess that, as described, receives balls arranged one behind the other along the longitudinal axis, the torque transmitting ability is reduced. A further disadvantage consists in that in the case of rapid movements, the balls abut the stops correspondingly violently, with damage being likely.
French Patent No. 1,373,752 discloses a longitudinal displacement unit wherein, in contrast to the above-described state of the art, no provision is made for freely setting the cage along the longitudinal axis between the first shaft element and the second shaft element. However, the cage is arranged between springs that are supported on stops in such a way that the cage is loaded toward a central position. The spring forces that are required to actually achieve the central position have to be correspondingly high, which means that smooth operational conditions are difficult.
It is an object of this invention to provide a longitudinal displacement unit that both provides smooth operational conditions within the range of the normal relative adjustment between the shaft elements along the longitudinal axis and prevents the components from being damaged toward the end positions.